Telephone-exchange system



E. S. GIBSON Filed Aug. 10, 1923 14 SheetS-Sheet 1 W f Mi /m Oct. 27,1925. 1,559,244

E. S. GIBSON TELEPHONE "EXCHANGE SYSTEM Filed Aug. 10, 1923 14 Sheets-Sht' 2 Oct. 27, 1925.

E. S. GIBSON TELEPHONE EXCHANGE SYSTEM Filed z- 1923 14 Sheets-Sheet s Mien/W [2M 3 G/bja/z fly C.

Oct 27,1925. 1,559,244

v E. s. GIBSON TELEPHONE EXCHANGE SYSTEM Filed Aug. 10, 1923 14 Sheets- Sheei 4 E. s. suasor:

TELEPHONE EXCHANGE SYSTEM Filed Aug. 10, l923 14 Sheets-Sheet 5 Q Q Q "3 Oct. 27.,1925- 1,559,244

E. 5. GIBSON TELEPHONE EXCHANGE SYSTEM IPile?1 1923 14 Sheets-Sheet 6 E. s. GIBSON TELEPHONE EXCHANGE SYSTEM v Filed Aug.--l0. 1 2 14 Sheets-Sheet '7 'Oct. 27, 1925: 1,559,244

11mm mun Oct. 27, 1925. 1,559,244

. E. S. GIBSON I 'rzLEm oNE EXCHANGE SYSTEM Filed Aug 10, 192.15 '14 sheets-sheet a oat. 27, 1925 E. S. GIBSON TELEPHONE EXCHANGE SYSTEM 14 Sheets-Shed 9 R5 NQ Filed Aug. 10, 1923 E. S. GIBSON TELEPHONE EXCHANGE SYSTEM Filed Aug. 10. 1 5 14 Sheets-Shut 1.0

. E. S. GIBSON 1 TELEPHONE. EXCHANGE SYSTEM 14 Sheets-Sheet 1 1 Filed Aug. 10, 1923 Wren/4r.

E. s GIBSON TELEPHONE EXCHANGE SYSTEM Filed Aug. 10, 1923 Oct. 27,1925 1, 9, 4 I E. S. GIBSON TELEPHONE EXCHANGE SYS T EI Filed Aug. 10, I923 14 Sheets-Sheet 14 Patented Get. 27, 1925.

UNITED STATES PATENT OFFICE.

EARL S. GIBSON, OF RIDGEVTOOD, NEW JERSEY, ASSIGNOB TO WESTERN ELECTRIC COMPANY, INCORPORATED, 033 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed August 10, 1923. Serial No. 656,742.

To all whom it may concern:

Be it known that I, EARL S. GlnsoN, a citizen ofthe United States of America, residing at Ridgewood, in the county of Bergen and State of New Jersey, have invented change systemsand more especially to sys-' tems wherein machine switching apparatus under the control of operators is employed for establishing connections.

The object of the invention is an improved system in which provision is made for completing connections to certain lines regardless of their busy or idle condition.

A feature of the invention relates to a system arranged for extending connect-ions over the lines of a group, such as private branch exchange lines, with provision for extending a subsequent call to one of said lines although the line may actually be busy at the time.

Another feature relates to a system of this character in which an operator by means at her disposal may aflfect the switching apparatus such that it disregards the busy condition of a trunk of a private branch exchange group and seizes one of the trunks thereof to extend a subsequent call. 7

Other features and advantages contemplated by this invention will be taken up in detail hereinafter andalso pointed out in the appended claims.

Considering the drawing Figs. 1 to 14, inclusive, taken in the order illustrated in 15 disclose enough of the details of a telephone system to give an understanding of the features of the present invention.

1 shows a trunk circuit incoming to the central oflice from a distant ofiice.

Fig. 2 illustrates an incoming selector switch of the coordinate type in which terminate trunks incoming from the distant oiiice.

Fig. 3 shows a second group selector switch to which connections are extended from the incoming switch in Fig. 2.

Fig. 4 illustrates a final or connector switch also of the coordinate type used for completing connections to called subscribers lines and to private branch exchanges.

Fig. 5 shows a second final selector switch similar to the one illustrated in Fig. at.

Fig. 6discloses anoperators keyboard, an impulse sending mechanism located in the same ofiice with the switches shown in Figs. 2,3, 4 and 5.

Fig. 7 shows a coordinate sender selector switch for extending the incoming trunks into connection with one of a number of register sender mechanisms.

Figs. 8, 9 and 10 illustrate details of one of the register senders.

Fig. 11 shows a sender connector device for associating the senders with the incoming marker.

Fig. 12 shows the incoming marker which controls a plurality of incoming selectors to which it is common and with which it is associable.

In the lower part of Fig. 13 is illustrated a multi-contact relay sender connector device for connecting the senders with the line marker. In the remainder of Fig. 13 and in Fig. 14 there is shown the line marker which is associable with the group selectors and connectorswitches of Figs. 3, d and 5.

The disclosure illustrates a terminating central oflice employing coordinate machine switches for completing connections to called subscribers lines. This office is arranged to cooperate with distant manual oiiices. Calls originating in the distant manual ofiices are routed over trunks which lead tothe terminating oflice and are under the control and supervision of cordless operators in the latter oflice. These incoming trunks from the originating oflices terminate in any suitable manner in the incoming automatic switches. It is the duty of thecordless operators to make the necessary assignments orally to the distant operators by means of an order wire and to bring about release of the equipment at the proper times. The cordless operators on receiving the designations orally, set them up on -the keyboard, with the result that these records are transferred by code impulses from the operators position to the register senders, which in turn, control the switches to complete the connections to the called lines.

It may happen that a call is received in the terminating ofiice from a long distance ofi'ice or toll point which desires connection to a private branch exchange trunk group in the terminating oiiice. Owing to the rela-- tive importance of such calls the cordle operator who attends to the assignment of the trunk may be pressing a special key, set up a no test condition. Because of this no test condition, the switches in the terminating office will seize upon a trunk in the private branch exchange group even though the same is busy at the time and thereby force the connection, whereas under other circumstances the switches would refuse to lake the connection.

General description of the system and appamtus.

The selective switches including the incoming selectors 200, group selectors 300, connectors 4-00 and 500 and sender selector switches 700 employee in th s system are of the coordinate tyze such as shown and de scribed in British Patent 1833236 to lVcstern Electric Company, Limited, allowed August 1923, and further shown and described in. U. S. Patent 1,517,331 to S. B. Vfilliams, issued December 2, 192

The trunk 100 incoming from the distant manual ofiice appears in the vertical row of contacts 201 of the incoming selector switch 200 and has access to all horizontal links 205, 206, etc. This incoming selector is shown in schematic form, only a limited number of the vertical rows of contacts and a limited number of the horizontal links beillustrated. A. second incoming trunk 212 is shown appearing in th vertical row of contacts 202. in the same manner other trunks incoming from the same or distant offices would appear in this and other equivalent incoming selector switches.

The incoming switch 200 also has a pinty of groups of outgoing trunks appean ing in rows 203, 204, etc. Each outgoing trunk is shown having an appearance before a single horizontal link. These trunks are multipled in order to appear before corresponding horizontal links in all of the remaining incoming selector switches controlled by the same marker mechanism. The trunks outgoing from the incoming selector switch are distributed among the ditlerent group selectors 300, one of these trunks 211 being shown in full.

A. convenient manner of arranging the group selector and connector switches is to make a division of the exchange into terminal line groups. For a 10,000 line ol'lice each terminal line group, for example, would have access to 2,000 different lines and would comprise a number of group selector and connector switches 300 and 400 and a single controlling line marker common to all of these switches. Each of the remaining four terminal line groups would likewise comprise a proper number of selector and connector switches and a line marker "for coiaiollina said switches. mccording to this plan the trunks outgoing from the in coming switches 200 would be distributed among the group selectors 300 in each of the remaining lino groups in order that any one of the 10,000 lines might be accessible.

Considering the terminal line group, the group selectors 300 are equipped with a number oi' groups of outgoing trunks which lead to the various groups of connector switches including switches 400 and 500. Two of these trunks and 325 are illustrated.

There will be as many connector switches as are necessary to accommodate the 2,000 subscribers lines, together with provision for many P. B. X. trunks as may be required. Each of the several direct subscribers lines is provided with a directory number and occupies a given position in one of the connector switches. leloreover, for each group or" P. B. X. trunks there is a single call-line which has a directory number identii ing the P. B. X. and which is located in the connector switches along with the regusubscribers lines. 'lhe several trunks .Ztl'

elonging to each private branch exchange group represented by a call number line are,

in other words, for each all-line there may be as man oing to the distant P. B. X. as desi ".icse trunks may be located in one or a num n& tor switch in which a pears the correspond call-line. Immediately that the call- :oe is sel ct connection through the group rotor and connector switches is released and automatically reestablishee through oup selector and the proper connector t e first id e W t trunk of the re- I l'; this first trunk is located ane connector switch with the ca l connector switch first used. However, the lirst idle trunk appear in a different connector switch, in which case, the reestablished connection leads to such other connector switch and thence to the selected id e P. B. X. trunk.

Considering the terminal line switching apparatus shown in the drawing there are illustrated a number of direct subscribers lines 434, 485, 530 appearing in the connector switches 400 and 500. There is also illustrated a P. B. X. call-line 438 appearing in the switch 400 and a number of P. B. X. trunks 436, 437, 439, 523 and 524 comprising the group represented by the call-line 438. It will be understood, as previously explained that all of these 1?. B. X. trunks may be located on a single P. B. Lil. switch or they may be distributed among several connector switches. All numbered lines including both direct subscribers lines and P. B. X. call-lines appear in the connector switches in groups or" vertical rows according to their numbers. F or instance, the vertical row of contacts 432 in the switch 400 represents a group of ten lines. Only three of these lines are illustrated in the drawing, the two subscribers lines 434 and and the B. X. call-line 438. In the second switch 500 (shown) the vertical row 520 represents another group of ten numbered lines. In like manner there will be as many of these vertical ten line groups in these and other connector switches as is necessary to accommodate the full 10,000 numbered lines. In addition to the numbered lines, P. B. X. groups also appear in vertical rows either exclusively or together with numbered lines as desired. The particular group shown occr, Ies all of the vertical row 483 in the switch 400 and alsoa vertical row 521' in the connector switch 500.

The connector switches are also provided with a number of groups of horizontal links, each group having access to all numbered lines of a particular units designation together with P. B. X. trunks. For example, the group of links containing the links 401 ant. 402 have access t the call-line 438 in the row 432, to the trunk 436 in the row 43?;

and also to other lines or trzniks in other rows (not shown). The horizontal test link 403 is associated with this group ofho zontal links and serves for test purposes hereinafter described. F or each of the remaining nine units designations, there is a group of these horizontal links having access to lines and trunks. in a similar manner the switch 500 has anumber of groups of horizontal links of which the links 501, 302 and 503 are a portion.

The incoming marker shown in Fig. 12 includes a series of test relays 1200 which serve to test the horizontal links in any of the incoming selector switches and also to test the outgoing trunks to which these links have access. The connecting device 1202 which comprises a number of multi-oontact relays 1204, 1205, 1206, etc. serves to connect the set of test relays 1200 with the proper group of outgoing trunks, the multicontact relays each being individual to a difierent group. Another connecting de vice 1201 consisting of multi-contact relays 1208, 1209, 1210, etc. serves to connect the marker testing relays with the individual incoming switches. Relays 1208, 1209, 1210, for instance, are individual to the particular switch 200 shown in the drawing. Relays 1220, 1221 and 1222 similarly are individual to another incoming selector switch.

The line marker shown in Figs. 13 and 14 includes a plurality of registers 1400, 1401 and 1402 which receive numerical records from the senders. It also includes the multi-contact rela translating device 1404 which is operated according tothe settings of these registers to select the magnets 415, 416, 508 and 509 individual to the different vertical rows of lines in the connector switches. Moreover, the line marker in cludes a multi-contact relay device 1403 which operates to associate the register 1401 with connecting devices 410 and 516 individual to the proper connector switch 400 or 500. The device 410., for example, consists of relays 411, 412, etc. and serves to associate certain test relays in the marker with the horizontal links of the group having access to the called lines of the desired units designation in the connector switch 400. In Fig. 18 a set of testing relays in the marker is shown, and these relays are associable through the multi-contact relay device 301, 302, with the groups oftrunks outgoing from the selector switch 300 and ether switches and also with the horizontal links of these selectors.

The operators position illustrated in Figs. 1 and 6 is equipped with a number of sets of keys 600, 601, 602 and 603 for recording the four digits of the called subscribers number or of the private branch exchange group. Moreover, the position is equipped with certain impulse generating mechanism whereby code impulses are originated in ac cordance with the record on the keyboard .and transmitted to the associated sender.

The operators keyboard is further provided with an assignment key 118 and a release key 119 individual to each of the incoming trunks, the keys mentioned being individual to the trunk 100. Also a no-test key 640 is provided by means of which the operator may set up the no-test condition to cause the seizure of a busy private branch eX change trunk.

Establishment of a connection to a group of private branch emclzange Mimics.

Consider that a connection is to be estab- Furthermore, it will be ass the number of the P. B. X. cal ."hich serves the desired groups of trun Assay mama 0/ an idle Hunt.

When tore operator in the distant ollicc receives the call she cor-miuni ates over order wire not shown to tor in the terznin and the operator the Co lyoperator being no depressed a i inaliy open. my 1' circuit is con'ipleted troin the winding of relay 108, key 118 to ground Rel cult from contact, windin of Relay 108 locks in a i ner left contact, conductor 12 inner left back c ntact ot relay 116, ("151M101 to ground through the left cont cts out key 119. Rela- 105 coinoletes a CilClliL from ground throu h its ri 'nt contact lain 120 to hata b 4 I u I I I ter The lain 3 120 is llluinlnated steadil .V 1 1 I. a Relay 108 also cioies a circuit rroni batter throu h the windin of reia T 109 outer b a 1 7 l\ l lel't contact oi relay 108, conductor lei), outer left contact 01' relay 610, right back contact 01' relay 609, right back contact 01 relay 608, to ground. Relay 109 operates in this circuit and associates the operators ke board and couion'ient shown 1n F10. 6

1 1 l 1 1 D with tne trunir 100, the keyboaru oeing common to a number or these trunk a Relay 198 locks throu h its inner upner contact, b I conductor 123, winding o'l; relay 609 to ground at the outer right back contact or relay 608. Relay 609 operates and relay 109 locks in this circuit. The operation or key 118 and the closing of the contacts or key 119 result 1n the closure 01 a circuit for operating the sender selector switch 700 to associate the trunk 100 with an idle register sender. This circuit may be traced from ground through the left contacts of key 119, conductor 12-1, conductor 125, inner right back contact of relay 112, conductor 126, lower back contacts of relay 110, conductor 127, winding of relay 713 to battery. Relay 713 is individual to the trunk 100 and serves to initiate the operation or the sender selector switch to associate an idle register sender with said trunk.

Relay 713, in operating, closes a circuit from battery, through the winding of relay 715, right back contact of relay 71 1, inner right contact of relay 713, conductor 734:, winding of relay 735 to ground.

Relays 71 1-, 715 and 716 enclosed within the broken rectangle pertain to the vertical group of contacts in the row 701 of the switch 700. These relays are brought into action whenever one of the trunks appearing in this row is seeking to be attached to a register sender.

Relay 715 completes a circuit ironi battery through the winding of relay 719, left contact of relay 715, condu-ctor 734,-, winding of relay 7 35, to ground. Relay 715 also closes a circuit from bat-te i hrough the left-hand winding of relay 716, right front contact of relay 715, left back contact of relay 717, outer right contact of relay 723 to ground through the winding of relay 735. Relay 16 at its outer left contact closes a circuit for relay 7 141. Relay 71% looks in a circuit through its winding and left contact and the contacts of relays 719 and 720 to ground. Relay 716 also closes a circuit from battery through its right winding and right contact, winding of relay 717, outer right back contact of relay 723 to ground through the winding of relay 735. Relay 717 operates and closes a circuit from battery through the winding of slow-to-release relay 722, outer right contact of relay 717, inner right back contact of relay 723 to ground through thewinding of relay 735. Relay 722 operates and closes a substitute holding circuit for relays 716 and 717 independent of relay 723. With relay 717 operated a circuit is closed from battery through the winding of the vertical magnet 729, outer right front contact of relay 716, left front contact of relay 717, and thence to ground as above traced. lilagnct 729 operates and prepares the contacts of the vertical row 701. Magnet 7 29 also closes a circuit from ground through its contact, conductor 736, left contact of relay 721, inner left contact of relay 716, outer right contact of relay 713, leithand winding of relay 712 to battery. Relay 712 is a group relay individual to the group of horizontal links including the links 707 and. 708.

Relay 712 operates and closes a circuit from battery through its right winding and right font contact, winding of relay 721' to ground over conductor 7 36. Relay 721 operates in this circuit.

Another circuit is closed from battery through the winding of the vertical magnet 731, brush 727 of the all-otter 726, contact of slow-to-release relay 725, left contact of relay 723, inner right front contact of relay 717 to ground through the winding of relay 7 it is assumed that the first sender to which the circuit 732 leads, is idle and that the allotter switch 726 is standing in a position to allot this particular sender as shown.

The allotter 726 has a position for each of the several senders appearing in the sender selector switch 700.

As above noted the vertical operating magnet 7 31 relative to the idle sender operates and prepares the contacts in the vertical row 704. Magnet 7 31, in operating, completes a circuit from battery through its winding and inner contact, winding of relay 723, inner right contact relay 717, winding of relay 735 to ground. Relay 723, however, being shunted by the circuit above traced does not operate at this time. Magnet 7 31, furthermore, closes a circuit from ground through its outer contact, conductor 740, brush 728 of the allotter, Contact and winding of stepping magnet 724, winding of relay 725 to battery. Magnet 724 operates, interrupts its own circuit and advances the brushes 727 and 728 to the neXt'set of terminals. If the following sender isidle, the allotter switch comes to rest, but if it is busy, the switch continues until an idle sender is found. the position shown, it opens the shunt around the relay 723 and this relay operates in series with magnet 7 31. The relay 723 opens the circuit of relay 722. Relay 722 being slow holds its armatures for an interval after the operation of relay 723 which is sufficient for certain, operations to take place as will presently be described.

During the interval measured by the release of relay 722 a circuit is closed from ground through the winding of relay 735, inner right front contact of relay 723, left contact of relay 721, left front contact of relay 712, back contact of relay 7 09, winding of the horizontal operating magnet 710 individual to the link 708 to battery. Mag net 710 operates and effects a connection between the link 708 and the incoming circuit and also between the link and the outgoing circuit 732.

At the time the vertical operating magnet 731 operates a circuit is closed from ground through the outer contact of said magnet, conductor 740, inner left back contact of re lay 805, winding of slow release relay 800 to battery. Relay 800 closes a circuit for relay 805. Relay 800 also looks in a circuit from battery through its winding and right contact, conductor 837, outer left contact of relay 838, outer left back contact of relay 832, conductor 839, outer right contact of relay 804, inner right contact of relay 805 to ground at the left front contact of relay 800.

Immediately that the connection is established through the sender selector 700 a circuit is closed from battery through the winding of the horizontal ma et 710, winding of relay 709, contacts of the switch 7 00, conductor 740, inner left front contact of relay 805, winding of relay 801 to ground lVhen the switch leaves at the inner left contact of relay 803. The magnet 710 is held energized in this circuit under the control of the sender after the above traced energizing circuit has been opened. Relay 709, however, being shunted for the time being remains deenergized to prevent the extension of the start circuit through to the next link in the group.

After the necessary interval has expired slow relay 722 releases and opens the circuit of relays 716 and 717. Relay 717 opens the circuitof relay 723 which releases and opens the original operating circuit through the winding of relay 709. Relay 709 thereupon operates in series with the magnet 710 in the substitute holding circuit. Relay 717 opens the circuit of the vertical operating magnet 729 and also the circuit of the operating magnet 7 31. These two magnets release and restore the associated rods to their normal positions. held by the maintained energization of the horizontal magnet 710.

At the time the-sender is first seized and relay 805 operates a circuit is closed from battery through the winding of slow-release relay 825, conductor 844, inner right back contact of relay 1004, thence over conductor 1011, conductor 843 to ground at the outer right contact of relay 805. Relay 825 operates and completes a circuit from battery through the winding of relay 824, left contact of relay 825, thence over conductor 847 to ground, through the middle right contact of relay 805. Relay 824 operates and conipletes a substitute holding ground on conductor 837. At the time the sender is seized another circuit is closed from battery through the winding of relay 809, conductor 861, inner right back contact of relay 903, to ground over conductor 843. Relay 809 The connection is y closes a circuit from battery through the 823 become deenergized, when subsequently,

the relay 903 operates on the receipt of the first digit from the operators keyboard.

As soon as the sender is attached to the trunk a circuit is completed from ground over conductor 740, through contacts of the sender selector, thence over conductor 741, right contacts of key 119, outer left contact of relay 103, winding of relay to battery and in parallel through the middle lower contact of relay 109, conductor129, winding of relay 610 to battery. Relay 110 at its lowermost contact opens the circuit of relay 713 resulting in the release of the controlling relays in the sender selector switch 700.

When the cordless operator receives the designation of the called subscribers line, which in the present case is number 1, 3, 2, 6, she proceeds to set this number up on her keyboard. Accordingly, she depresses the No. 1 key 632, the No. 3 key 633, the No. 2 key 63 and the No. 6 key 685. These keys are of the locking type and remain depressed until they are released by the key release magnets 60 i, 605, 606 and 607. The contacts 636, 63'4", 638 and 639 are common to the rows 600, 601, 602, and 603, respectively and operate when any key in these rows is depressed. Vfhen a k y in each row has been operated, as above mentioned, a circuit is completed from ground through the contacts'636. 637, 638 and 639 through the inner right front contact of relay 61.6, conductor 6&1, inner lower contact of relay 169, thence through the Winding of relay 116 and in parallel through r upper Kile r: contact ot relay 110 and the lower v.-'inding of relay 115 to battery. Relay 115 compl tes a circuit from battery through the lamp 121, inner lower front contact of said relay, inner right contact. of relay 116, inner lower front contact of relay .116, through the interrupter 130 to ground. The interrupter 130 causes the lamp 121 to flicker. Relay 116 releases the relay 108, which in turn, releases the relay 105 to open the circuit of lamp 120. Relay 108 releases atthis time since the operator has already released the assignment key 118 to open the original circuit therefor.

Transfer 0 f mrmercal record 250 the sender.

Another circuit is completed from ground through the contacts 636, 637, etc, thence through the left contact of relay 609. wind. ing of relay to battery. Relay 629 opcratesand prepares the mechanism in Fig. 6 for transniiitting codes of impulses in accordance with the depressed keys to establish the record of the P. B. X. call line on the registers of the associated sender. Re lay 629 completes a circuit from ground through the right l ack contact of relay 666, right front contact of relay 609, inner left contact of relay 619, conductor. 651, middle right contact of relay 629, inner right back contact of relay 627, outer right contact of relay 626, inner right contact of relay left back contact of relay 627, left-hand windings of relays 628 and 627 to battery. Relay 626 operates in this circuit but relay 627 being marginal does not receive sutli cient current to energize. Relay 628, in operating, completes a circuit from battery. through the left-hand Winding of relays 621' and 628, right-hand windino' o."

inner right contact of relay .ndeo. conductor 651. winding of relay 62?,

shunted by the above circuit operate. Relay 628 completes rein grounri through its outer act, conductor 6 1-2, contact of outer right back contact of relay 61 ing of relay to battery. Relay crates and closes a circuit from through winding and inner left contact, winding of relay 62l to ground oyer conductor Relay 621, however, being shinned does not o'ierate at this time.

also completes a circuit from ground through the outer right contact of relay 610, conductor 643, inner right contact of relay 629, conductor 6 14-, left back con; tact of relay 624, winding of relay 628 to battery.

Relays 623 and 62sare constructed to operate and releaseslowly and in conju ction with each other they serve to measure ter- Yals of time for the purpose of creating and transmitting impulses in accordance with the settings of the keys on the peratoi keyboard to represent different digits of the wanted line. Relay 623, therefore, operates slowly in the above traced circuit and on completing its operation closes a circuit from battery through the winding of relay 624-, inner left contact of relay 623 to the wounded conductor 6%. Relay 62 i energizes in this circuit and operates slowly. ll hen relay 62 i is fully operated a circuit is closed from battery through he windiir and normal contact of relay 622, outer ri, front contact of relay 62% to the grounded conductor Relay 622 operates and looks through its inner left front contact to ground over conductor 6&4. When relay 62E- coinpletes its operation it closes a circa from battery through a resistance and middle right contact directly to the ground n conductor 644-. This circuit being in shunt of the relay 623, the latter re commences to release slowly. l i hen relay .623 is fully released it closes a circuit from battery through its right back contact directly to the grounded conductor 641% in shunt of the relay 624. Therefore. the relay 62st commences to deenergize slowly. ln this manner the relays 622 and 624-. operate in succession and release in succession to measure intervals of time.

While the relays 623 and 624 are relcasinej a circuit is completed from ground or the positive pole of battery through the outer right contact of relay 622, conductor 650, 1 outer left contact of relay 629, conductor 672. right normal contacts of relay 630, conductor 652, middle upper contact of relay 109, conductor 131, contacts of the sender a selector 700, conductor 743, normal contacts My lll) 

